Balancing Chemical Equations

Balancing Chemical Balancing Chemical EquationsEquations

Mrs. PaganoMrs. Pagano

Physical Science 10 CPPhysical Science 10 CP

What are Chemical Equations?What are Chemical Equations?

A chemical equation is an equation that A chemical equation is an equation that uses the chemical formulas of the atoms uses the chemical formulas of the atoms being combined in the chemical reactionbeing combined in the chemical reaction

Chemical Equation ExampleChemical Equation Example

The chemical equation forThe chemical equation for

Methane + Oxygen = Carbon Dioxide + WaterMethane + Oxygen = Carbon Dioxide + Water

Is writtenIs written

CHCH44 + O + O22 CO CO22 + H + H22O O

Reactants and ProductsReactants and Products

CHCH44 + O + O22 CO CO22 + H + H22OO

In a chemical equation, the chemical In a chemical equation, the chemical formulas written on the formulas written on the leftleft side of the side of the arrow are called arrow are called ReactantsReactants

The reactants form the The reactants form the ProductsProducts which are which are written on the written on the rightright side of the arrow side of the arrow

Reactants Products“Give” or “Yield”

Balanced Chemical EquationsBalanced Chemical Equations

In order for a chemical equation to be In order for a chemical equation to be balanced, the amount of atoms of each balanced, the amount of atoms of each element on the right-hand side of the element on the right-hand side of the equation must match the number of atoms equation must match the number of atoms of each element on the left.of each element on the left.

Is this Chemical Equation Is this Chemical Equation Balanced?Balanced?

K + HK + H22O KOHO KOH22 4 atoms 4 atoms

What About This One?What About This One?

2K + 2H2K + 2H22O 2KOH + HO 2KOH + H22

8 atoms 8 atoms

Coefficient

= 2 (K)

Subscript

Conservation of MassConservation of Mass

All chemical equations must be balanced All chemical equations must be balanced to follow the to follow the Law of Conservation of MassLaw of Conservation of Mass

The Conservation of Mass Cont.The Conservation of Mass Cont.

2Mg + O2Mg + O22 2MgO 2MgO Notice that there are Notice that there are equalequal numbers of numbers of

magnesium and oxygen atoms in the magnesium and oxygen atoms in the product product andand the reactants in the equation the reactants in the equation aboveabove

The total mass of the reactants will always The total mass of the reactants will always equal the total mass of the product/s in a equal the total mass of the product/s in a balanced equation =balanced equation =The Conservation of The Conservation of Mass LawMass Law

Let’s Try One TogetherLet’s Try One Together

Identify the reactants and products and Identify the reactants and products and write the chemical formula for:write the chemical formula for:

Magnesium and oxygen react to form Magnesium and oxygen react to form magnesium oxidemagnesium oxide

Mg + O MgOMg + O MgOReactants Products

Balance the Equation One Atom at Balance the Equation One Atom at a Timea Time

AtomAtom ReactantsReactants ProductsProducts BalancedBalanced

MgMg 11 11 YesYes

OO 22 11 NoNo

Mg + O2 MgO

So, How Do We Balance Oxygen?So, How Do We Balance Oxygen?

Mg + OMg + O22 MgO MgOThere are two atoms of oxygen on the left, but only one on the right. To get the correct number of oxygen atoms on the product side we need to add a coefficient of 2 to MgO

Mg + O2 2 MgO


MgMg 11 22 nono

OO 22 22 yesyes

Now We Need To Balance MgNow We Need To Balance Mg22Mg + OMg + O22 2MgO 2MgO


MgMg 22 22 yesyes

OO 22 22 yesyes

We have to add another coefficient to Mg on the left side to equal the amount of atoms on the right side. Adding the coefficient 2 will give us the correct number of magnesium atoms on both sides.

Last Step: Confirm the Equation is Last Step: Confirm the Equation is BalancedBalanced


MgMg 22 22 yesyes

OO 22 22 yesyes

2Mg + O2 2MgO

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Balancing Chemical Equations